Abstract: Weight-related problems including obesity, poor eating behaviors, and inadequate physical activity are prevalent among emerging adults and have adverse physical and psychosocial consequences. Obesity is one of the most significant public health problems facing young people today. Emerging adulthood is one of the most rapid periods of growth and development as young people undergo identity formation and changes in interpersonal influences (becoming more independent from parents and more aligned with friends). College freshmen are at particular risk as they generally have very poor diets and low levels of physical activity, which have been associated with increased risk of overweight/obesity into adulthood. Recently NIH has called for the development of multi-level studies to better understand and address obesity and other weight-related problems, and there is a lack of research focusing on the role of friends in population-based samples of college students. It is crucial to identify longitudinal mechanistic and contextual factors among friendship networks of young people at greatest risk for obesity and weight-related problems. The identification of multi-level predictors of key weight-related behaviors and outcomes among friendship networks will guide the development of more comprehensive and effective interventions to promote healthy eating, physical activity and weight status in emerging adults. Thus, the primary aim of this study is to assess the role in which friendship networks are involved in nutrition and physical activity behaviors and risk for excess weight gain among college freshmen. To accomplish this aim, we will use a mixed-methods approach, capitalizing on the unique opportunities at Arizona State University which includes high percentages of students from ethnic/racial minority (40%) and low-income (40% are Pell Grant recipients) backgrounds who are at greatest risk for obesity. We will collect qualitative and multiple sources of quantitate data, each complementing the other, to longitudinally track how friendships are created, and better describe the mechanisms by which friends are prospectively associated with weight-related behaviors and outcomes. We will also collect data on contextual aspects of the students' networks (e.g., type of friendship, race/ethnicity) to capture information that can be used to create targeted interventions. Innovative research methodologies (i.e., ecological momentary assessments and university databases) will be utilized to survey friends of participating students across an academic year to explore friends' potential impact on freshmen's weight-related outcomes. The proposed study builds upon our research team's experience, and expands to address new areas that are emerging as important in addressing obesity and related problems in young people, creating an ideal environment for a young investigator to become an independent researcher. Findings from this innovative, comprehensive study on the role of friends and social networks will guide the development of more effective interventions to prevent and treat weight-related behaviors and outcomes among college students.